Rick Santorum, who late polls say may be leading today in the Iowa caucus, is standing by his position that traditional marriage between a man and a women should be protected by a constitutional amendment – even if that invalidates same-sex marriages that have already occurred.

(Photo: REUTERS/Rick Wilking)

Republican presidential candidate Rick Santorum waits to be introduced to supporters at a campaign stop at the Button factory restaurant in Muscatine, Iowa December 29, 2011.

Currently, same-sex marriage is valid in seven states, but civil unions are legal in many others. The 1996 Defense of Marriage Act, signed into law by former President Bill Clinton, defines marriage as between a man and a woman, but allows each state to define marriage in their own constitution.

“No, I think marriage has to be one thing for everybody,” Santorum told Chuck Todd in an interview for NBC Nightly News. “You can’t have 50 different marriage laws in this country – you have to have one marriage law.”

The former Pennsylvania senator said that if a constitutional marriage amendment is enacted, same-sex marriages now valid in some states would become invalid, touching off a firestorm of criticism by liberals.

Santorum’s thoughts on the validity of same-sex marriages under a federal marriage amendment are in direction contrast to his chief rival, former Massachusetts Gov. Mitt Romney, who in an interview last month said that if a federal marriage amendment were enacted, then existing same-sex marriages should remain intact.

Santorum disagrees. “I would love to think there is another way of doing it, but I have grave concerns about the Supreme Court and the courts in the future and what they will do to marriage, just like they have done to abortion.”

Dr. Richard Land, who chairs the Ethics and Religious Liberty Commission and is an advisory board member with The Christian Post, points out that a constitutional amendment has a much greater impact than a law.

“Yes, an federal constitutional amendment defining marriage as between one man and one woman would be significant,” Land told The Christian Post. “Remember, constitutional amendments have repealed slavery, prohibition and given women the right to vote. I believe a marriage amendment would invalidate any existing same-sex marriage.”

Santorum went on to say that amendments that define marriage as between one man and one woman have passed in 32 out of 32 states where the question was placed before the voters on the ballot.

“When people understand the real consequences of what happens when we change the definition of marriage, people say, ‘I want to be tolerant, I want people to live the lives they want,’ and I’m the same way,” Santorum said. “But same-sex couples can contract for just about anything they want to with except direct government benefits. Marriage is a special union in our society – a special relationship.”

But for states that do recognize same-sex marriage, the larger issue would be how states or the federal government would handle existing marriages. In other words, would same-sex couples be forced to divorce?

“Well, their marriages would be invalid,” said Santorum.

In reaction to Santorum’s comments, gay marriage activist are saying a federal marriage amendment would amount to “forced divorce” in states that currently recognize same-sex marriages.

“What Santorum is pushing, however, is tantamount to forced annulment or divorce -- even though divorce is something he and the Christian right acknowledge is harming marriage -- which would result in thousands of families legally dissolved or broken up in six states where gay and lesbian couples have married,” wrote Michelangelo Signorile, the Editor-at-Large of HuffPost Gay Voices in The Huffington Post.

In a new PPI poll, Santorum is leading on the eve of the Iowa caucuses with 24 percent, followed by Gingrich with 16 percent and Romney and Paul with 15 percent.